1. Field of the Invention
This invention relates to lighting systems and, more particularly, a greenhouse lighting system which has a low operating cost and which grows plants at an accelerated rate.
2. Description of the Prior Art
Artificial light has long been used both experimentally and commercially to provide supplemental or total light for plants. The light has generally been of a spectrum which is most suitable for plant growth produced by relatively efficient lamps which have a relatively high lumen per watt ratio. These systems generally utilize a number of point light sources spaced apart above the plants. The number of lamps used in these conventional lighting systems as well as the spacing of the lamps from each other and from the plants is selected to place a specific intensity of light on the plants. However, light received by the plants is not constant since the plants closer to the light sources receive light of a higher intensity. The variations in light received by the plants result in a non-uniformity of growth or a "wave formation." One technique which has been employed to eliminate "wave formation" has been to continuously move the light sources above the plants so that the average intensity of the light received by the plants is relatively constant. These systems generally mount a lamp on an elongated track with the lamp continuously moving along the track at a constant rate. Alternatively, the lamp is mounted in a fixed position, and the illumination angle of the lamp is varied. It should be emphasized that in these systems the light is moved at a fairly high rate of change and although it is well known that artificial light will accelerate plant growth, many attempts have been made to optimize the growth rate from artificial light by practicing a variety of techniques for directing the light onto the plants. Some experimenters have determined that light applied in a relatively short burst or flash will stimulate growth at a reduced energy cost since the light is on for only a portion of the time period. A serious problem with this technique is the general unavailability of lights which will operate at the flashing speed required. To alleviate this problem to some extent, experimenters have resorted to a complicated and highly sophisticated system of special light sources, controls, and other devices to provide the necessary flashing or intermittent light. Such systems are extremely expensive and unduly complex.